# Alpine Linux Quick Reference

*Package management, services, networking, Docker base image*

> Source: Alpine Linux Documentation (wiki.alpinelinux.org) · MIT

## Package Management

### apk Basics

```
apk update               # refresh package index
apk upgrade              # upgrade all packages
apk add curl git vim     # install packages
apk del curl             # remove a package
apk search nginx         # search for packages
```

### Package Info

```
apk info                 # list installed packages
apk info -a nginx        # detailed package info
apk info -L nginx        # list files in package
apk policy nginx         # show available versions
```

### Virtual Packages

```
# Install build deps as a group, remove later
apk add --virtual .build-deps gcc musl-dev
make && make install
apk del .build-deps
```

### Repositories

```
# /etc/apk/repositories
https://dl-cdn.alpinelinux.org/alpine/v3.20/main
https://dl-cdn.alpinelinux.org/alpine/v3.20/community
@edge https://dl-cdn.alpinelinux.org/alpine/edge/testing
```

## Services

### OpenRC Service Management

```
rc-service nginx start    # start service
rc-service nginx stop     # stop service
rc-service nginx restart  # restart service
rc-service nginx status   # check status
```

### Runlevel Management

```
rc-update add nginx default   # enable at boot
rc-update del nginx default   # disable at boot
rc-update show               # list all services
rc-status                    # show running services
```

### Runlevels

| Command | Description |
|---------|-------------|
| `sysinit` | System initialization (filesystems, clock) |
| `boot` | Basic system services (networking, syslog) |
| `default` | Normal services (web servers, daemons) |
| `shutdown` | Shutdown tasks |

## Configuration

### Key Config Files

| Command | Description |
|---------|-------------|
| `/etc/apk/repositories` | Package repository URLs |
| `/etc/hostname` | System hostname |
| `/etc/network/interfaces` | Network interface config |
| `/etc/conf.d/` | Service-specific configuration |
| `/etc/motd` | Message of the day |

### System Setup

```
setup-alpine             # interactive full setup
setup-timezone           # set timezone
setup-keymap             # configure keyboard layout
setup-hostname myhost    # set hostname
```

### Timezone

```
apk add tzdata
cp /usr/share/zoneinfo/US/Eastern /etc/localtime
echo "US/Eastern" > /etc/timezone
apk del tzdata          # optional: remove to save space
```

## Networking

### Interface Config

```
# /etc/network/interfaces
auto eth0
iface eth0 inet dhcp
# --- static ---
iface eth0 inet static
  address 192.168.1.10/24
  gateway 192.168.1.1
```

### Network Commands

```
ip addr show             # show IP addresses
ip route show            # show routing table
ip link set eth0 up     # bring interface up
setup-interfaces         # interactive net config
```

### DNS & Firewall

```
# DNS: /etc/resolv.conf
nameserver 1.1.1.1
nameserver 8.8.8.8
# Firewall
apk add iptables
iptables -L -n           # list rules
```

## Users

### User Management

```
adduser alice             # create user (interactive)
adduser -D -s /bin/sh bob # non-interactive, set shell
deluser alice             # delete user
passwd alice              # set/change password
```

### Groups & Sudo

```
addgroup devs             # create group
addgroup alice devs       # add user to group
apk add doas              # lightweight sudo alternative
# /etc/doas.conf
permit persist alice as root
```

### System Users

```
adduser -S -D -H -s /sbin/nologin myapp
# -S system user  -D no password
# -H no home dir  -s no shell
```

## Disk & Storage

### Filesystem Commands

```
df -h                    # disk usage summary
du -sh /var/log          # directory size
lsblk                    # list block devices
mount /dev/sda1 /mnt     # mount device
umount /mnt              # unmount
```

### LBU (Alpine Local Backup)

```
# For diskless/data modes — persist changes across reboots
lbu status               # show uncommitted changes
lbu commit               # save changes to boot media
lbu list                 # list backed-up files
lbu include /etc/myconf  # add path to backup
```

### Disk Setup

```
setup-disk               # interactive disk install
setup-disk /dev/sda      # install to specific disk
# Modes: sys (traditional), data, diskless
```

## Docker Base Image

### Why Alpine for Docker

| Command | Description |
|---------|-------------|
| `~5 MB base image` | vs ~80 MB for Debian slim |
| `musl libc` | Smaller than glibc (some compat issues) |
| `apk package manager` | Fast, no cache by default |
| `Minimal attack surface` | Fewer packages = fewer CVEs |

### Minimal Dockerfile

```
FROM alpine:3.20
RUN apk add --no-cache python3 py3-pip
COPY app.py /app/
CMD ["python3", "/app/app.py"]
```

### Multi-Stage Build

```
FROM golang:1.22-alpine AS builder
WORKDIR /src
COPY . .
RUN go build -o /app
FROM alpine:3.20
COPY --from=builder /app /app
CMD ["/app"]
```

### Common Gotchas

| Command | Description |
|---------|-------------|
| `--no-cache` | Always use to keep image small |
| `musl vs glibc` | Some binaries need gcompat package |
| `No bash by default` | Use /bin/sh or apk add bash |
| `Timezone missing` | Install tzdata if needed |

## Common Patterns

### Install Build Tools

```
apk add --no-cache build-base   # gcc, make, etc.
apk add --no-cache python3-dev  # Python headers
apk add --no-cache linux-headers # kernel headers
```

### Cron Jobs

```
# Add a cron job
echo "*/5 * * * * /usr/local/bin/task.sh" \
  | crontab -
rc-service crond start
rc-update add crond default
```

### Enable SSH

```
apk add openssh
rc-service sshd start
rc-update add sshd default
# Config: /etc/ssh/sshd_config
```

### Upgrade Alpine Version

```
# Edit /etc/apk/repositories: change v3.19 → v3.20
apk update
apk upgrade --available
sync && reboot
```